A:Answer It all comes down to whether or not the person that purchased and returned it already redeemed it. If they did, it's gone, if they didn't it's still there.
It's tied to the system. Most likely the serial number.
You redeem it during set up.
When I first got mine, I swapped out the SSD for a 2 TB before ever setting it up. I then did the install of the operating system with the restore from Asus. During setup, it offered the three month premium game pass, and I took it.
I ended up deciding to switch to a 4 TB the next day and went through the steps of swapping out the drive and once again installing the operating system. This time it did not offer the three month premium game pass because I had already redeemed it. Which means it knew that this ROG Xbox Ally had already gotten it.
No way to guarantee one way or another.